The present invention relates to sheets of laminated loop material adapted to be cut into discrete loop patches for use in hook and loop fastening components for low cost applications, particularly disposable diapers and the like.
Nonwoven loop materials intended for use in low cost applications, particularly in respect to disposable garments such as surgical gowns or disposable absorbent articles, such as diapers, have increased in popularity in recent years. This has resulted in intensive development efforts to provide a material that is both high performance for the intended user and low cost. The focus of these efforts has been on providing a low cost loop material which adequately functions to provide a resealable mechanical closure for a limited number of repeated applications. For these uses, it is not necessary that the loop material have sufficient integrity to enable long term repeat attachment and release cycles or resistance to washing. However, the loop material should provide a relatively high peel and secure closure for a limited number of use cycles. Knitted, woven or stitch-bonded and like traditional fabric materials have been proposed in these limited use garment loop applications. Generally, these traditional fabric materials provide more integrity than is needed for the limited use garment field, and are more expensive than required. Lower cost versions of these traditional loop fabric materials have lower fiber density per unit area and hence are lower performance. In response, it has been proposed in a number of patent applications to use nonwoven fabrics of a wide variety of types to form relatively low cost but high, short term performing loop materials. For example, U.S. Pat. No. 5,256,231 is an early patent that proposed the use of a nonwoven web, such as produced by a carding process, to form a loop material. In this patent, the nonwoven web is fed between two corrugating members which provide the nonwoven web material with loft or z-direction orientation. The corrugated web is given integrity in the x and y directions by extruding a thermoplastic backing layer onto tip portions of the corrugated nonwoven material, which is still maintained at this point in the corrugated state between at least one of the corrugating members and a nip backing member. Optional additional layers can be brought in, which additional layers can be printed to provide desired print patterns on the loop material. The process described in this patent provides highly advantageous low cost loop structures. However, particularly when bringing in an additional printed backing layer, the loop material tends to become excessively rigid, particularly when the loop materials are formed from the preferred polypropylene resins described. When a loop material is intended to be used in a disposable, absorbent garment, softness is an extremely important property in order to avoid discomfort for the wearer, as well as providing a conformable form-fitting garment. The use of polyethylene fibers and films or bi-component bonding fibers and the like can provide loop materials with increased softness, however, often at a significant cost increase, increased problems with manufacturability, and/or decreased loop performance. From the standpoint of cost and performance, it is preferable that the nonwoven web material be formed primarily from polypropylene fibers. However, polypropylene fibers present difficulties in providing a soft loop material in that a polypropylene backing or backing film layer is generally required in order to provide adequate fiber anchorage, and polypropylene backing films are relatively stiff.
U.S. Pat. No. 5,614,281 describes a method for forming nonwoven loop materials by micrexing or creping a specific nonwoven material while simultaneously bonding it to a film or nonwoven backing material. The specific end product loop materials exemplified are described as being soft where the nonwoven web is formed from melt-spun fibers of a random copolymer of propylene and ethylene and the film backing layer is a blend of polypropylene with about 16% polyethylene. However, this process suffers from the disadvantage that the nonwoven loop material must be prebonded in order to survive the creping process which process results in significant shear forces on the web during creping. Prebonding decreases the penetrability of the web to hook materials, decreasing performance in the hook and loop laminate structure. The shear forces can also cause fibers to shed or become dislodged in the web. Creping also results in a web with uneven or irregular corrugations which results in uneven bonding to the backing layer. Further, the polypropylene film backing material specifically suggested is still relatively stiff.
A number of other patents have proposed the use of nonwoven materials for use in forming loop structures including, for example, U.S. Pat. No. 5,032,122, wherein a nonwoven web or series of filaments are bonded to a material in an oriented unstable state. The unstable oriented material is subsequently allowed to recover gathering the nonwoven web or fibers to form upstanding loop structures. WO 96/04812 describes a similar method for forming a loop material where the backing is an elastomeric material and the nonwoven web forming the loops is bonded to the backing with a specific bond pattern. This loop material would suffer from numerous disadvantages, such as being generally dimensionally unstable when elastic materials are provided as the backing; relatively low levels of bonding to, e.g., a nonwoven polypropylene loop material; require high cost backing materials; and are somewhat difficult to manufacture. A similar approach is described in WO 95/33390 where the backing is an elastomeric adhesive material. This elastomeric adhesive film described allegedly provides an unstable film material capable of retracting to form the attached nonwoven web into loops and also provide a certain level of bonding to the nonwoven material. This approach would generally suffer from the identical problems associated with the WO 96/4812 published application described above and also has generally poor adhesion properties.
Other nonwoven loop fastening materials are described in U.S. Pat. Nos. 5,470,417 and 5,326,612 which relate to non-corrugated, nonwoven materials having specific bonding patterns and layer structures used to form loop materials.
Despite the extensive levels of activity and development efforts in using nonwoven fabrics for forming loop materials, there is still a need for providing a low cost, high performance nonwoven loop material which is also easy to manufacture, has good fiber to backing adhesion, and is soft and conformable with additionally having the ability to be bonded to a further layer having desirable properties such as a printing pattern while remaining relatively soft.